Please Help! There's Annoying Teal Blotches on Certain Colors

Looks like a screen issue, but before going and replacing the screen hook the Chromebook up to an external monitor and make sure it isn’t the same there. This laptop lacks internal HDMI, so you need an adapter. You can get a USB-C>DP adapter (or straight USB-C), but neither DP or straight USB-C is a "common" option on "consumer grade" monitors -- you usually only find it on high end monitors from Dell, HP, BenQ and ASUS (gaming or PROART). For compatibility, the best way to test is with a USB-C>HDMI adapter. Your average monitor from Acer/HP/Dell/low-end Asus WILL OFTEN LACK USB-C OR FULL-SIZED DP.
Testing tip: You can sometimes see if someone has a high end display you can hook it up to for a brief test with the right cable, but these people aren't using Chromebooks; we use high end business class notebooks from HP and Dell, or mobile workstations (HP Z/Precision). NOT ALL OF IT IS, but a lot of our equipment is so good, you can usually bet on having things like DP or USB-C PD with video output. If I scored one and someone asked to test with it onsite, I’d be fine with it, especially if I had a USB-C/DP equipped HP Z, IPS Ultrasharp or LG IPS monitor like that. BUT I'd forewarn them these things run their Chromebook over in terms of color output performance with DCI-P3 or Adobe sRGB (95%+ color gamut) so the Chromebook will look washed out.

If the screen is bad, a lot of these Chromebooks use the same parts but you also will run into a issue with part cost vs. whole unit replacement due to how cheap a used equivalent Chromebook often is with major parts like screens - batteries and power jacks are less of a problem but anything major totals most Chromebooks out and pushes them into "BER" cost ranges.
However, you can always buy an identical (or at least, very similar) parts units with issues like a enterprise lock that the previous owner refuses to remove for these major parts - these cost almost nothing since they’re brick. For the Chromebook you have (HP ARM MediaTek), these use an iDP LCD; not an LVDS like Intel HP Chromebooks. THESE PANELS CANNOT BE INTERCHANGED. That said, a Dell or Lenovo donor may work (confirm the screen type first!!!) but it will have a Dell DP/N or Lenovo FRU, not an HP Spare#. You won't know on the outside anyway, though.

If you can’t find a donor, it looks like HP FINALLY abandoned LVDS on these MediaTek Chromebooks :-). This is excellent since iDP isn’t a nightmare to work with to replace a bad LCD like LVDS. As an example of why I don't mind kicking LVDS out and letting the door hit it -- I can put a Lat 7400 LCD in a 840 G5/G6 too, with a tab transfer -- couldn't do that on a LVDS E7440/E6440. They’re both standard implementations, but the connectors vary on LVDS so often you have to do a lot more research on compatibility - whereas iDP tends to just work. Skip the Intel models as donors, as many of them are LVDS :-(. HP Part# is M15719-001.

Tip: See if you can find a bare IPS panel from LG, Innolux, or AUO (If you can find it, a used/new Samsung LTN LCD panel -- LG IPS is king; Samsung is nearly as good). I did it with a Samsung IPS LCD (LTN) on my 6300U 840 G3 to replace the awful Innolux SVA display. My Lat 7490 came with the FHD LG IPS panel out of the box, and it’s even better then the Samsung LTN panel in my 840 G3. Samsung no longer makes normal LCD panels, so whatever is left is what we have then we need to move to LG or Innolux.